The present invention relates to apparatus for the precision placement of electronic components on a hybrid circuit substrate and, more particularly, to the placement of small articles such as semiconductor chips, capacitor chips and integrated circuit chips on a ceramic substrate which has been preprinted with a thick film conductor pattern.
As the name suggests, hybrid circuits are a combination of discrete and integrated circuit techniques. As in integrated circuits, conductors, resistors and conductive lands are printed on a ceramic substrate. In thick film technology, the printed elements are generally several mils thick. Then discrete chips are precisely positioned over the conductive lands and subsequently bonded in position in a manner to complete the electrical circuit. The printed conductor lands provide a pattern which precisely matches to the corresponding conductive portions of the chips that connect to the circuit elements within the chip as by solder. The bonded chips and substrate, with an exposed lead frame, are frequently encapsulated in toto in a potting compound for protection against physical and environmental damage. Use of unencapsulated chips on the circuit board allows for the manufacture of physically smaller circuits than those where discrete components which have already been encapsulated have their leads inserted into circuit boards fitted with receiving connectors or into predrilled holes wherein the leads are subsequently cut and clinched. A primary advantage of chips is their small size, some being nearly microscopic. Chips in the order of 0.030 by 0.030 inches square and 0.010 thick and solder connection portions and conductor lands in the order of 0.005 inches in height and width, and spaced apart by similar distances, are not uncommon. Nevertheless, for the hybrid circuit technique to be successful, the small chips must be positioned and oriented such that when placed on the substrate, all solder connection portions and lands are properly connected without error. This requires a high degree of precision in positioning which was achieved in early development of these techniques by human operators using microscopes and tweezers.
The need for automatic, rapid, precise, repeatable and low cost means to position and bond chips on substrates was apparent if the burgeoning requirements of mass production in the electronics industry were to be met. Generally speaking, in the apparatuses which have been developed in the past, the chip or other small component, e.g., beam leaded components, are picked up and placed by a hollow probe device which is connected to a vacuum source. When the probe touches the upper flat surface of the chip, the vacuum within the probe holds the chip against the probe end. The chip is then raised, translated to the substrate, and lowered onto the substrate. Several of the cross-references listed above illustrate prior attempts to improve the precision of placement of the components onto the circuit board by combining centering fingers with the vacuum probe. Thus, while the probe supports the component by vacuum, the fingers center the component relative thereto prior to placement. Permanent bonding of chip to substrate is accomplished in some systems while the probe continues to hold the chip. In other systems, the conductive lands are pretreated with some form of tacky adhesive or soldering flux. The probe gently presses the chip surface into the tacky adhesive so that electrical contact is made with the conductive lands. Then the vacuum within the probe is released and the chip remains adhered to the substrate as the probe is withdrawn. A positive gas pressure within the probe is sometimes used to separate the chip from the probe.
Broadly speaking, other prior art designs fall generally into two categories. In the first category, the substrate and the chip are both separately, fixedly and precisely oriented and located. A transfer mechanism, usually utilizing a vacuum probe as described above, travels an invariable, repetitive path to pick up the chip and place it at one selected position on the substrate. Then, a new substrate and new chip are fed into their respective positions and the operation repeats. In the second category, the chips start out with a degree of disorientation, for example, at random in a vibratory feeder bowl. The feeder bowl, in the known manner, operates to bring each chip in turn to a precise position. From that point, the design is similar to the first category; although additional steps to angularly orient the chip may be required intermediate the feeder bowl and the precisely located substrate. Still other prior art has combined these two categories.
Another device for centering a chip on the vacuum probe prior to placement is disclosed in U.S. Pat. No. 3,982,979. Therein, the rectangular component is supported from below on a probe using a slight vacuum. The probe is centered in a four-sided cavity having the form of an inverted truncated pyramid. As the probe is lowered, the component makes contact with the cavity walls and becomes aligned thereto; at the same time, the component is centered on the probe. A substrate is precisely positioned above the cavity, and the probe is raised to position the centered component on the substrate from below.
U.S. Pat. Nos. 4,437,232, and 4,135,630, as well as German Pat. No. 2,944,810, illustrate a failure of the prior art to provide controlled, positive pressure of the centering fingers onto the component. Further, spring closing of the finger onto the component fails to provide the accuracy needed for controlled, repeatable squaring, centering and orienting by the fingers. Additionally, the prior art references do not teach orienting a component according to the requirements of the circuit board layout such that orientation occurs during gripping of the component by the centering fingers.
What is needed is an apparatus for placement of chips, e.g., integrated circuit chips, capacitor chips, on a preprinted circuit board substrate of the thick film construction. In accordance with an automated program, the apparatus should be capable at a single work station of placing a plurality of different chips of various types and physical and electrical sizes on a substrate with a high degree of precision as is required to complete the circuit. Precise location of stored chips should not be required; the apparatus should orient and center each chip after selection and prior to placement.
For adapting such a pick and place apparatus to various sets of components having different configurations, the prior art has concerned itself with totally changing or substantially modifying the pick and place head according to the configuration of the chip being handled resulting in a greater expense and down time for making such changes. What is needed is a method and apparatus for high speed automated adapting of a particular pick and place head to components of various configurations and sizes.